<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>
  </head>
  <body>
    <script>
      // info = {键（属性名）:值（属性值）}
      const info = { age: 20 };
      // age属性在info中存在吗？或info中有age属性吗
      const x = "age";
      if (x in info) {
        console.log("存在");
      } else {
        console.log("不存在");
      }
    </script>
  </body>
</html>
